JPH10244646A - Laminated polyester film for capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film which shows high dielectric strength and heat dimensional stability and outstanding adhesion with a vacuum-deposited metal layer. SOLUTION: This laminated polyester film for a capacitor comprises an A layer which originates from polyester (A) with a higher specific resistance at a melting time than the specific resistance of polyester B at the melting time and shows the specific resistance of 1.0×10<8> Ω.cm or more, formed on both faces of a B layer originating from polyester (B) with a particulate content of 2.0wt.% or less and the specific resistance of not more than 2.0×10<9> Ωcm at a melting time. In this case, the thickness of the B layer should account for 30% or higher of the overall thickness of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laminated polyester film for a capacitor. Specifically, the present invention
The present invention relates to a laminated polyester film capable of producing a film having excellent withstand voltage characteristics and thermal dimensional stability at a low cost and giving high electrical characteristics when used for a capacitor dielectric.

[0002]

2. Description of the Related Art Polyester films are widely used as industrial materials for magnetic tapes, packaging, plate making and the like because of their excellent mechanical properties, heat resistance and electrical properties. Among them, for capacitors, the demand for capacitors manufactured from polyester films that can be miniaturized is rapidly increasing with the miniaturization of electric devices.

In particular, in recent years, with the development of electronic equipment and the like, it is required to improve the characteristics of such polyester films for capacitors. One of the requirements for higher characteristics is withstand voltage characteristics. Capacitor films require high electrical insulation properties, but are usually used as thin films of 15 μm or less, so if coarse foreign substances are present in the film or if the film is damaged, insulation defects will occur. As a result, the capacitor characteristics are greatly reduced. For this reason, the polyester used as a raw material of the film for a capacitor is limited to a range that does not have such a problem, and the productivity and cost are sacrificed at present.

[0004] On the other hand, in order to reduce thickness unevenness and increase the production speed during the production of a polyester film, usually,
In the step of cooling and solidifying the molten sheet, an electrostatic printing method is used. In order to improve the effect of such a cooling method, it is known that it is effective to lower the specific resistance of the polyester at the time of melting. For this purpose, a method of including a metal component in the polyester is used. ing. However, in the case of a capacitor film, it is necessary to increase the specific resistance during melting in order to increase the insulation resistance of the obtained film, and the above-described method cannot be used. There has been a demand for a method that simultaneously satisfies both productivity and insulation resistance characteristics to a high degree.

[0005] On the other hand, with the increase in the amount of capacitors used, the demand for cost reduction has become even stronger, and the necessity of expanding the range in which the raw materials can be used has increased. Specifically, it has become essential to use recycled materials, but such materials have a high impurity content, which causes a problem that the withstand voltage characteristics are reduced.

[0006] In addition to these properties, the film has other necessary properties, such as long-term reliability represented by, for example, heat resistance and moisture resistance. That is, the metallized polyester film is
It has a drawback that the adhesiveness between the base film and the deposited metal, particularly the adhesiveness in a high-temperature and high-humidity environment, that is, the so-called wet-heat resistance is poor. Therefore, when the capacitor is placed under high temperature and high humidity, there is a problem that moisture permeates at the interface between the base film and the vapor-deposited metal, and the capacitance of the capacitor decreases with time.In terms of long-term stability, There is a need for such improved wet heat resistance.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a film which is excellent in withstand voltage, thermal dimensional stability and adhesion to a metal layer to be deposited.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above problems, and as a result, have found that a laminated film made of polyester whose specific resistance at the time of melting is in a specific range, the film having a thickness of The present invention has been found to be able to be produced at low cost when specific requirements are satisfied, and to have excellent characteristics when used as a capacitor dielectric, thereby completing the present invention.

That is, the gist of the present invention is that the content of particles is 2.0% by weight or less and the specific resistance at the time of melting is 2.0 × 1
The specific resistance at the time of melting is higher than the specific resistance at the time of melting of the polyester (B) and is 1.0 × 10 ⁸ Ω · cm or more on both surfaces of the layer B derived from the polyester (B), which is less than 0 ⁹ Ωcm. A laminated polyester film having a layer A derived from polyester (A), wherein the thickness of the layer B accounts for 30% or more of the total thickness of the film.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyester constituting the film of the present invention is a polyester obtained by using an aromatic dicarboxylic acid or an ester thereof and a glycol as main starting materials, and 80% or more of the repeating structural units are ethylene terephthalate units or ethylene-2,6-. Refers to a polyester having naphthalate units. Then, other conditions may be contained as long as the conditions do not deviate from the above range.

As the aromatic dicarboxylic acid component, for example, in addition to terephthalic acid and 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxyethoxy) Benzoic acid and the like can be used. As the glycol component, other than ethylene glycol, for example, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol,
One or more of neopentyl glycol and the like can be used.

In the present invention, both the A layer and the B layer are mainly made of polyester, but the polymer composition of each may be the same or different. For example, the B layer is made of polyethylene terephthalate, and the A layer is made of polyethylene terephthalate. It may be a copolymerized polyethylene terephthalate containing any copolymerized component or a mixture thereof. The polyester film of the present invention prevents the occurrence of scratches during film production,
For the purpose of giving the film slipperiness and improving handling,
The polyester is made to contain particles to form appropriate protrusions on the film surface. Examples of such particles include inorganic particles such as calcium carbonate, calcium phosphate, silica, kaolin, talc, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, and molybdenum sulfide, crosslinked polymer particles, and oxalic acid. Organic particles such as calcium and precipitated particles formed during the polymerization of polyester can be exemplified.

The content of the particles in the layer B is 2.0% by weight or less, preferably 1.0% by weight or less, more preferably 0.5% by weight based on the polyester forming the layer B.
It is as follows. If the particle content is more than 2.0% by weight, the insulating properties of the film deteriorate, and the withstand voltage characteristics of a capacitor deteriorate. The average particle size of the particles in the layer B is preferably 0.01 to 5 μm, and more preferably 0.1 to 3 μm. When the particle size of the particles increases, a problem occurs that the insulating properties of the film deteriorate. When the average particle size exceeds 5 μm, the insulating properties tend to deteriorate. There is no lower limit of the particle content in the B layer, and a layer containing no particles may be used. However, the particles may be contained in order to mix a recycled material, and the lower limit is usually 0.00%.
It is about 1% by weight.

On the other hand, it is preferable that particles are also contained in the layer A, and the particles to be contained preferably have an average particle size of 0.1.
It is desirably in the range of 01 to 3 μm, more preferably 0.05 to 2 μm, and not larger than the average particle size of the particles in the B layer. The content is preferably 0.01 to 5% by weight, more preferably 0.1 to 3% by weight, particularly preferably 0.2 to 2% by weight based on the polyester constituting the layer A.
It is. Further, the content of the particles in the layer A with respect to the polyester in the layer A is preferably larger than the content of the particles in the layer B with respect to the polyester in the layer B. If the particles in the A layer are too large or the content is too large, problems such as a decrease in insulation due to surface roughening, or particles falling off the film surface to cause insulation defects may occur. . On the other hand, if the particles are too small or the amount is insufficient, the improvement of the slip property tends to be insufficient, and a scratch is generated on the film surface,
Again, this may cause insulation defects.

Two or more kinds of these particles may be blended in each layer, and particles of the same kind but different in particle diameter may be blended. In any case, it is preferable that the average particle diameter of all the particles contained in each layer and the total content satisfy the above-mentioned range. The thickness of the layer A is usually in the range of 0.1 to 3 μm, preferably 0.2 to 2 μm. On the other hand, the thickness of the layer B is at least 30%, preferably at least 40%, more preferably at least 50% of the total thickness of the film. When the thickness of the B layer is less than 30%, the effect of cost reduction is reduced, and the effect of cooling by electrostatic application during film production is hardly obtained, so that the productivity is reduced.

In the present invention, the intrinsic viscosity of the polyester constituting the layer A is preferably higher than the intrinsic viscosity of the polyester constituting the layer B. The effect of improving the insulating properties of the film of the present invention can be highly realized when such requirements are achieved. In particular, when the intrinsic viscosity of the polyester in the layer A is 0.60 or more, preferably 0.62 or more, high insulating properties are achieved.

The layer B has a specific resistance of 1.2 × when melted.
10 ⁹ Ω · cm or less, preferably 1.0 × 10 ⁹ Ω · c
m, more preferably less than 7.0 × 10 ⁸ Ω · cm, in the step of cooling and solidifying the molten polymer sheet during film production, by using an electrostatic application cooling method. Thus, the effect of improving the thickness uniformity can be sufficiently obtained. On the other hand, the layer A needs to be derived from a polyester having a higher specific resistance at the time of melting than that of the layer B. When the specific resistance of the layer A at the time of melting is low, the insulation resistance characteristics of the film become insufficient, and the withstand voltage characteristics of the obtained capacitor deteriorate. Further, the layer A has a specific resistance of 1.0 × 10 ⁸ Ω · cm or more, more preferably 5.0 × 10 ⁸ Ω · cm or more, particularly preferably 1.0 × 10 ⁹ Ω · cm or more when melted. Which is derived from polyester. In order to prevent the withstand voltage characteristic of the film from being significantly deteriorated, the layer B has a specific resistance at the time of melting of 1.0 × 10 ⁸ Ω · cm or more, and more preferably 2.0 × 1 ⁸ Ω · cm.
0 ⁸ Ω · cm or more is desirably derived from a polyester and particularly 5.0 × 10 ^{8 Ω} · cm or more.

In recent years, there has been an increasing demand for cost reduction of the film, and it is particularly effective to use 30% by weight or more of the recycled material as the material for the B layer. Such a recycled material may be a recycled material of the film of the present invention itself or a recycled material obtained from another product. Such a recycled material does not have a high specific resistance at the time of melting, or may contain a small amount of foreign matter to lower the electrical properties of the film. Therefore, it is preferable that the recycled material is not contained in the A layer. Content is 8
The content is preferably 0% by weight or less.

In the present invention, as additives other than the above-mentioned projection-forming agent, if necessary, antistatic agents, stabilizers, lubricants, crosslinking agents, antiblocking agents, antioxidants, coloring agents, light blocking An agent, an ultraviolet absorber, and the like may be contained in the layer B or the layer A or both layers as long as the capacitor characteristics are not deteriorated.

The film of the present invention is preferably provided with a coating layer on at least one of the film surfaces in order to enhance the adhesion to the deposited metal. Examples of the coating agent constituting the coating layer include polyester, polyamide, polystyrene, polyacrylate, polycarbonate, polyarylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, polyvinyl alcohol, and polyurethane. Examples of such resins include resins of a system and the like, and copolymers and mixtures of these resins. Among these, preferred coating resins are polyester resins, polyacrylate resins and polyurethane resins, most preferably polyurethane resins. When a coating agent containing a polyurethane-based resin preferably in an amount of 30% by weight or more, more preferably 50% by weight or more, extremely high adhesiveness and long-term wet heat resistance can be obtained.

The resin used as a coating agent in the present invention is preferably a water-based coating agent for safety and hygiene purposes. However, a water-soluble or water-dispersible resin may be used without departing from the scope of the present invention. An organic solvent may be contained as an auxiliary. When water is used as the medium, a coating agent forcibly dispersed with a surfactant or the like may be used, but a hydrophilic nonionic component such as polyethers or a cation such as a quaternary ammonium salt is preferable. It is a self-dispersible coating agent having a functional group, and more preferably a water-soluble or water-dispersible coating agent having an anionic group. A water-soluble or water-dispersible coating agent having an anionic group is one in which a compound having an anionic group is bonded to a resin by copolymerization, grafting, or the like, and sulfonic acid, carboxylic acid,
It is appropriately selected from phosphoric acid and salts thereof. The amount of the anionic group in the water-soluble or water-dispersible coating agent having an anionic group is preferably in the range of 0.05 to 10% by weight. If the amount of the anionic group is less than 0.05% by weight, the water solubility or dispersibility of the resin may be poor. If the amount of the anionic group exceeds 10% by weight, the water resistance of the undercoat layer after application may be poor. , Absorb moisture and the films stick to each other,
In some cases, the wet heat resistance may be reduced.

The coating agent of the present invention includes a urea-based methylol or alkylol as a cross-linking agent for improving the adhesion (blocking property), water resistance, solvent resistance and mechanical strength of the coating layer. , Melamine-based, guanamine-based, acrylamide-based, polyamide-based compounds, epoxy compounds, aziridine compounds, block polyisocyanates, silane coupling agents, titanium coupling agents, zirco-aluminate coupling agents, peroxides, It may contain a heat- and photoreactive vinyl compound, a photosensitive resin, or the like.

In order to improve the sticking property and the sliding property, silica, silica sol, alumina, alumina sol, zirconium sol, kaolin, talc, calcium carbonate, calcium phosphate, titanium oxide, inorganic fine particles are contained in the coating layer.
Barium sulfate, carbon black, molybdenum sulfide, antimony oxide sol, etc., as organic fine particles, polystyrene, polyethylene, polyamide, polyester, polyacrylate, epoxy resin, silicone resin,
It may contain a fluorine resin or the like. Further, if necessary, it may contain an antifoaming agent, a coating improver, a thickener, an antistatic agent, an organic lubricant, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like. .

A known method is used to apply the above-mentioned coating solution to the polyester film, and the coating solution may be applied in the film manufacturing process or may be applied after the film is manufactured. In particular, from the viewpoint of uniformity of the coating thickness and production efficiency, a coating method in the film manufacturing process is preferable. As a method of applying in the film manufacturing process, a coating liquid is applied to a polyester unstretched film, a method of sequentially or simultaneously biaxially stretching, applying to a uniaxially stretched polyester film, and further perpendicular to the uniaxial stretching direction. Method to stretch in the direction, or applied to the biaxially stretched polyester film,
Further, there is a method of stretching in the horizontal and / or vertical directions.

The thickness of the coating layer is preferably in the range of 0.005 to 0.5 μm, more preferably 0.01 to 0.3 μm.
m, particularly preferably 0.03 to 0.1 μm. It is preferable that the thickness of the coating layer be reduced in view of a demand for miniaturization of the capacitor. In particular, the coating layer thickness is 0.5μ
If it exceeds m, the electrical characteristics may be degraded. On the other hand, when the thickness of the coating layer is less than 0.005 μm, there is a tendency that coating unevenness and coating slippage tend to occur.

It is preferable that the film of the present invention further satisfies specific conditions of shrinkage characteristics. Specifically, when the shrinkage stress in the longitudinal direction of the film satisfies the following expression, excellent characteristics can be obtained. it can.

[0027]

S150 <120 g / mm ² Smax <500 g / mm ² (in the above formula, S150 is a shrinkage stress value per unit sectional area of the film at 150 ° C., and Smax is 150 ° C.)
It indicates the maximum value of the shrinkage stress value within the temperature range below the melting point of the film.)

When S150 is 120 g / mm ² or more, the dimensional stability of the film tends to be inferior, and when it is used as a capacitor dielectric, the electrical characteristics may deteriorate. S
150 is preferably less than 100 g / mm ² , more preferably less than 70 g / mm ² . Further, the shrinkage stress value has a maximum value (Smax) within a temperature range of 150 ° C. or more and the melting point of the polyester, but in the present invention,
When Smax is less than 500 g / mm ² , the dimensional stability is excellent, and the capacitor characteristics can be more highly satisfied. Smax is preferably less than 400 g / mm ² , more preferably less than 350 g / mm ² .

The total thickness of the laminated film of the present invention is usually in the range of 2.0 μm to 15 μm. When the thickness exceeds 15 μm, it tends to be difficult to reduce the size of the capacitor, and the shrinkage characteristics of the film are originally small, so that the effect of the present invention may not be sufficiently exerted. The thickness is preferably 12 μm or less, more preferably 10 μm or less. On the other hand, the total thickness is 2.0 μm
If it is less than 30, the cost reduction and the withstand voltage property improving effect obtained as a laminated film may not be sufficiently obtained. In the case where the coating layer is provided, when the film becomes thinner, the proportion of the thickness of the coating layer relatively increases, so that the effect of improving the electrical characteristics may be insufficient. The lower limit of the total thickness of the film is more preferably 3.0 μm.

The laminated film of the present invention is preferably obtained by a coextrusion method. In general, lamination of a film, extrusion lamination, coating, and the like are also known as a lamination method of a film. However, in the present invention, a co-extrusion method which is the simplest and is an excellent lamination method without a decrease in electrical characteristics of the film is used. It is preferable to employ it. Of course, a method of coating on the surface of a film obtained by coextrusion is preferably employed. Use of the coextrusion method has many advantages, such as no problem such as peeling between the A layer and the B layer, and the production can be performed at low cost. Next, the method for producing the film of the present invention will be specifically described.

The polyester raw materials constituting the layer B and the layer A are supplied to separate extruders, respectively, melt-extruded at a temperature not lower than the melting point of the polyester, and are laminated in a molten state. And extruded as a molten sheet so as to form layer A on both sides. For lamination of the molten polymer, a feed block, a multi-manifold die, or the like can be used. Next, the molten sheet is quenched and solidified on a rotary cooling drum so as to have a temperature equal to or lower than the glass transition temperature, thereby obtaining a substantially amorphous unoriented sheet. In this step, it is preferable to use an electrostatic application cooling method in order to increase the adhesion between the molten sheet and the cooling drum, mainly for the purpose of improving the film thickness uniformity and increasing the production speed.

The obtained sheet is stretched in the biaxial direction to form a film. By setting the stretching and heat treatment conditions in appropriate ranges, the shrinkage characteristic, which is a feature of the film of the present invention, can be achieved. The biaxial stretching condition is specifically described. First, the unstretched sheet is stretched in the first axial direction so that the birefringence (Δn) is usually 0.06 or more, preferably 0.08 or more. The stretching temperature range is usually from 70 to 150 ° C., and the stretching ratio is usually from 2.5 to 6 times, and the desired birefringence is obtained by appropriately combining the temperature and the magnification. Stretching can be performed in one step or two or more steps. Next, the second axis direction, that is, once cooled the uniaxially oriented film below the glass transition point in the direction orthogonal to the first axis direction, or without cooling, for example, preheated to a temperature range of 80 to 150 ° C., Under the same temperature, usually 2.5 to 5 times, preferably 3.0 to 5 times
The film is stretched 4.5 times to obtain a biaxially oriented film.

It is preferable that stretching in the first axial direction is performed in two or more steps, because good thickness uniformity can be achieved. Further, a method of further stretching in the longitudinal direction after the transverse stretching is possible, but in any case, it is preferable to set the total stretching ratio in the longitudinal direction to 3.5 times or more. The film thus obtained is usually treated for 1 second to 100 seconds and 1
80 ° C to 250 ° C, preferably 200 ° C to 2 ° C
Heat treatment is performed in a temperature range of 40 ° C. At this time, re-stretching may be performed in the longitudinal direction, the lateral direction, or both directions during or after the heat treatment step.

In the present invention, in order to obtain a specific range of shrinkage stress characteristics of the film, the film may be subjected to a heat treatment step in the longitudinal direction or the transverse direction, or in both directions, in order to obtain a shrinkage stress characteristic in a specific range.
%, Preferably in the range of 3 to 15%, or a method in which the film is subjected to off-line thermal relaxation under low tension. However, the off-line heat treatment method is disadvantageous in terms of cost due to the increase in the number of steps, the impurities are likely to be mixed and the withstand voltage is often lowered, and the tension is extremely increased in the case of a thin film of about 6 μm or less. And there is a problem that stable processing is difficult.

On the other hand, the shrinkage rate can be reduced by using a method of increasing the heat treatment temperature during film production. However, when such a method is used, the electrical properties of the polyester film, particularly the dielectric loss properties, are deteriorated. It is not preferable when used as. Specifically, the heat treatment temperature is 240
If the temperature exceeds ℃, the film density becomes too high, and high electrical characteristics may not be obtained. On the other hand, 180 ° C
If it is less than 1, the heat shrinkage of the film becomes large, causing a dimensional change in a step of receiving heat during the production of the capacitor, causing problems such as deterioration of the productivity of the capacitor and deterioration of the capacitor characteristics such as withstand voltage. In any case, in the present invention, a method of achieving a specific shrinkage stress characteristic by performing a heat treatment while relaxing the film is preferable.

The deposited film of the present invention preferably has a film density of 1.40 so as not to deteriorate the electrical characteristics.
50 g / cm ³ or less, more preferably 1.4020 g
/ Cm ³ or less, particularly preferably 1.4000 g / cm 3
The following is assumed. In order to satisfy such characteristics, the temperature of the heat treatment step is appropriately selected. 1.40 film density
If it exceeds 50 g / cm ³ , the dielectric loss tends to increase, and the characteristics of the capacitor may deteriorate.

In the case where a coating layer is provided in the present invention, a method for applying the coating solution is, in particular, applying a coating solution to a uniaxially stretched polyester film stretched in the first axial direction by a roll stretching method and subjecting it to appropriate drying or drying. It is preferable that the uniaxially stretched film is stretched immediately in the second axial direction without heat treatment, and then heat-treated. According to this method, the coating layer can be dried simultaneously with the stretching, and the thickness of the coating layer can be reduced according to the stretching ratio, and the uniformity of the thickness is improved. Can also be made very strong. A film which is advantageous in terms of cost and is suitable as a substrate for a capacitor dielectric can be produced at low cost. The coating layer in the present invention may be provided on only one side of the polyester film, but is preferably provided on both sides. Also, apply different coating agents on the front and back of the film,
Different characteristics can be provided.

The film may be subjected to a chemical treatment or a discharge treatment before application in order to improve the coating property and adhesion of the coating agent to the film. It is particularly preferable to perform the corona discharge treatment in terms of treatment efficiency, cost, and simplicity of the treatment. Also,
In order to improve the adhesiveness, coatability, and the like of the coating layer of the biaxially stretched polyester film of the present invention, the coating layer may be subjected to a discharge treatment after the formation of the coating layer.

When the film of the present invention is used as a dielectric of a capacitor, a method of depositing metal on one or both sides of the film to provide electrodes is preferably used.
Aluminum, palladium, zinc, nickel, gold, silver, copper, indium, tin, chrome,
Titanium and the like can be mentioned, and a particularly preferred metal is aluminum. The above-mentioned metals include metal oxides. The thickness of the metal deposition film is preferably in the range of 10 to 2000 °.

As a method of vapor deposition, a vacuum vapor deposition method, a sputtering method or the like is usually used. After the metal deposition, a surface treatment of the deposited metal layer or a coating treatment with another resin may be performed. When a capacitor is produced using the obtained metal-deposited polyester film as a dielectric, two capacitors are superposed and wound (including the winding of a double-sided metal-deposited polyester film and another film including the polyester film of the present invention). ) Or by laminating many pieces to make a capacitor element,
According to a conventional method, for example, hot pressing, taping, metallikon, voltage treatment, both end face sealing, lead wire attachment, and the like are performed. Of course, it is not limited to these.

[0041]

The present invention will be described below in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. In addition, the evaluation method in an Example is as follows. In Examples and Comparative Examples, “parts” means “parts by weight”. (1) Average particle size (μm) of particles Particle size distribution analyzer (SA-CP, manufactured by Shimadzu Corporation)
Integrated volume fraction 5 in equivalent spherical distribution measured by type 3)
The particle size of 0% was defined as the average particle size.

(2) Specific resistance at the time of polymer melting (Ω · c)
m) The polymer was melted at 285 ° C. to remove bubbles contained therein, and then two stainless steel electrodes were inserted. 10
After holding for 1 minute, a DC voltage of 1 kV was applied between the electrodes,
The current value immediately after application was read, and the specific resistance was calculated according to the following equation.

[0043]

(Equation 3) (Where I is the current value (A), S is the area of the electrode (cm)
² ), t is the distance (cm) between the electrodes)

(3) Film Thickness (μm) Approximately 100 films are cut into 10 cm × 10 cm squares, and the weight is measured. Then count the number,
The film thickness is calculated from the film density, the total film area and the weight.

[0045]

(Equation 4)

(4) Thickness of each layer of the film The thickness was calculated from the melt extrusion amount of the resin forming each layer. However, prior to calculation, polyester containing fine particles,
A polyester not containing was co-extruded under the same conditions, and the thickness constitution of the obtained laminated film was measured. That is, a small piece of the laminated film was fixed with an epoxy resin, cut with a microtome, and the cross section of the film was observed with a transmission electron microscope. The thickness ratio between the portion containing the fine particles and the portion not containing the fine particles was measured. Based on the result of the measurement, the thickness configuration of the co-extruded laminated film was obtained.

(5) Shrinkage Stress Characteristics A sample film was cut into a strip having a width of 5 mm and a length of 70 mm, and one end was set on a minute load detector and the other end was set on a fixed chuck. The position of the chuck was adjusted so that the film did not sag, the position was fixed immediately before the tension was generated, and the measurement was started with the initial tension set to 0 g. The temperature around the sample film was raised at a rate of 5 ° C./min, and the relationship between the generated shrinkage stress and the temperature in the immediate vicinity of the film was drawn with a curve to determine the shrinkage stress per initial cross-sectional area of the film. That is, S150 and Smax are the 150 of the obtained curve.
° C and shrinkage stress values at the peak. (6) Film Density (g / cm3) Measured by a density gradient tube method using a mixed solution of n-heptane and carbon tetrachloride. The measurement was performed at a temperature of 25 ° C.

(7) Evaluation of electrical characteristics (i) Withstand voltage characteristics Measurement was performed according to JIS C-2319. That is, using a 10 kV DC withstand voltage tester, 23 ° C., 50%
Under an atmosphere of RH, the voltage was increased at a rate of 100 V / sec, and the voltage when the film was broken and short-circuited was read.

(Ii) Change in Capacitor Characteristics (Manufacture of Capacitor) The film was deposited in a stripe shape having a margin in the longitudinal direction of the film (the width of the deposited portion was 8 mm,
The polyester film was slit into a 4.5 mm wide tape having a left or right margin of 0.5 mm width. Each of the obtained left margin and right margin vapor-deposited polyester films, one by one, was wound together to obtain a wound body. At this time,
2 so that the deposition part protrudes by 0.5 mm in the width direction.
The films were shifted and wound. This roll is heated to a temperature of 1
Pressing was performed at 40 ° C. and a pressure of 50 kg / cm 2 for 5 minutes.
Metallicon is sprayed on both ends of the wound body after pressing, leads are attached, and an impregnated layer of liquid bisphenol A type epoxy resin, and a package with a minimum thickness of 0.5 mm by heating and melting the powdery epoxy resin To form a film capacitor having a capacitance of 0.1 μF.

(Measurement of change in capacitance) While applying a DC voltage of 60 V / μm between the electrodes of the capacitor, the temperature was set to 60 ° C.
It was left for 1000 hours in an atmosphere of a humidity of 80% RH, and a capacitance change rate using the initial capacitance as a reference value was determined. That is, the value obtained by subtracting the initial capacitance from the capacitance after 500 hours was divided by the initial capacitance and expressed as a percentage.

(Change in Dielectric Loss) The obtained capacitors were left in an atmosphere of 150 ° C. for 24 hours, and the dielectric loss characteristics at the initial stage and the dielectric loss characteristics after standing were compared. The dielectric loss characteristics were evaluated by performing measurements in a temperature range from room temperature to 160 ° C. That is, the following criteria were used to evaluate the temperature at which the dielectric loss rapidly rises and the maximum value of the dielectric loss shown in the range of 100 ° C to 160 ° C.

Rank A: Almost no change in characteristics after standing at 150 ° C. Rank B: Dielectric loss is slightly higher or rise temperature is lower. Rank C: The change in the dielectric loss is large or the variation in the numerical value is large.

(Iii) AC Withstand Voltage An AC voltage of 1 kHz was applied between the electrodes of the capacitor obtained above, and the time t until dielectric breakdown occurred was measured. The same measurement was performed by changing the applied voltage V, and the relationship between V and t was plotted. The applied voltage at t = 15 hours was defined as the AC withstand voltage. The value of the AC withstand voltage at 100 ° C. and 25
The values at ° C. were compared and evaluated according to the following criteria.

Rank A: Even at 100 ° C., the decrease in AC withstand voltage is small and good. Rank B: AC withstand voltage is slightly lowered at 100 ° C., but there is no practical problem. Rank C: The AC withstand voltage at 100 ° C. is greatly reduced, and there is a practical problem.

Example 1 (Production of polyester film raw material) 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.09 part of calcium acetate monohydrate were placed in a reactor, heated and heated, and methanol was distilled off to transesterify. The reaction was carried out, the temperature was raised to 230 ° C. over 4 hours from the start of the reaction, and the transesterification was substantially completed.

Next, 0.6 parts of silica particles having an average particle diameter of 0.3 μm were added as an ethylene glycol slurry. After the addition of the slurry, 0.06 parts of phosphoric acid and 0.04 parts of antimony trioxide were further added, and the reaction system was gradually reduced in pressure, the temperature was increased, and the polycondensation reaction was performed for 4 hours. a) was obtained.

Similarly, polyester (b) containing 0.2 parts of silica particles having an average particle diameter of 1.2 μm and having an intrinsic viscosity of 0.65, and polyester (c) containing no particles and having an intrinsic viscosity of 0.68 I got Also, a polyester (d) having an intrinsic viscosity of 0.65 was obtained in the same manner as the polyester (b) except that the amount of phosphoric acid to be added was changed. The specific resistance of the polyesters (a), (b), (c), and (d) at the time of melting is 2.5 × 10 ⁹ Ω · cm and 3.5 × 10 ⁹ Ω · c, respectively.
m, 6.0 × 10 ⁹ Ω · cm, 8.0 × 10 ⁸ Ω · cm
Met.

(Production of polyester film) A raw material obtained by mixing 70 parts of polyester (a) and 30 parts of polyester (b) was used as a raw material for layer A, and polyester (d) was used as a raw material for layer B, and dried by a conventional method. Then, the mixture was supplied to a separate extruder, melted at 290 ° C., laminated by a feed block, co-extruded into a sheet, and quenched on a cooling roll using an electrostatic contact method to obtain an amorphous sheet. . The thickness ratio was set to be 10/80/10 as A layer / B layer / A layer. The obtained sheet was stretched 2.5 times in the longitudinal direction at 86 ° C. using the roll stretching method, and further stretched 1.5 times at 78 ° C. Next, the film was guided to a tenter, stretched 4.0 times in the horizontal direction at 110 ° C, and heat-treated at 150 ° C. Further, the film was guided to a separate tenter and heat-treated at 235 ° C. while relaxing 8% in the transverse direction, to obtain a laminated biaxially oriented polyester film having a total thickness of 9 μm.

Example 2 The film and scrap obtained in Example 1 were melt-extruded and formed into chips to obtain a recycled material (e). Except that 50 parts of the recycled material (e) and 50 parts of the polyester (c) and the polyester (d) were mixed and used as the layer B, a total thickness of the film was obtained in the same manner as in Example 1. A 9 μm laminated biaxially oriented polyester film was obtained.

Example 3 (Synthesis of polyurethane for coating layer) Terephthalic acid 650
Part, 650 parts of isophthalic acid, 1,4-butanediol 4
80 parts and 450 parts of neopentyl glycol were used as starting materials to obtain a polyester polyol.
20 parts and 270 parts of dimethylolpropionic acid were added to obtain a carboxyl group-containing polyester polyol. 160 parts of tolylene diisocyanate was added to 1880 parts of this polyester polyol to obtain an aromatic polyester polyurethane solution. The solvent was removed while adding the obtained solution to an aqueous ammonia solution to obtain an aqueous dispersion of an aromatic polyester polyurethane (A).

A laminate having a total thickness of 9 μm was prepared in the same manner as in Example 2 except that the above-mentioned aqueous dispersion of copolymerized polyurethane was applied to both sides of the uniaxially stretched film after stretching in the longitudinal direction. A biaxially oriented polyester film was obtained. The thickness of the coating layer was 0.05 μm on both sides.

Example 4 In place of tolylene diisocyanate used in the preparation of polyester polyurethane for coating agent in Example 3,
An aliphatic polyester polyurethane aqueous dispersion (B) was obtained in the same manner as in Example 3 except that 4'-dicyclohexylmethane diisocyanate was used. The weight ratio of the aromatic polyester polyurethane (A) and the aliphatic polyester polyurethane (B) produced in Example 3 was 50 parts / 5.
The coating treatment was performed as 0 parts. The raw material of the layer A is a mixture of 90 parts of the polyester (a) and 10 parts of the polyester (b), and the raw material of the layer B is the same as in Example 2 and has a thickness ratio of 5/90.
/ 5. The film forming conditions were the same as those in Example except that the heat treatment step was continued in the same tenter as in the transverse stretching, the relaxation rate was set to 10% in the step of heat treatment at 232 ° C., and the heat treatment at 200 ° C. was performed with 2% relaxation. In the same manner as in Example 3, a biaxially oriented laminated polyester film having a thickness of 9 μm was obtained.

Example 5 A biaxially oriented film having a coating thickness of 0.04 μm and a film thickness of 8 μm was prepared in the same manner as in Example 3 except that the film was not subjected to the relaxation treatment during the heat treatment at 235 ° C. Obtained. Comparative Example 1 A single-layer biaxially oriented film having a film thickness of 9 μm was obtained in the same manner as in Example 1 except that the raw material for layer A in Example 1 was used. The obtained film was not inferior in characteristics as a film for capacitors, but the production speed in the molten sheet cooling process during production did not increase, the productivity was inferior, and inexpensive raw materials were used. However, the cost was disadvantageous.

Comparative Example 2 A single-layer biaxially-oriented film having a film thickness of 9 μm was obtained in the same manner as in Example 1 except that the raw material for the layer B in Example 1 was used. The properties of the obtained film as a capacitor were inferior. Comparative Example 3 The thickness ratio of layer A / layer B / layer A in Example 2 was 40/2.
Except having set it to 0/40, it carried out similarly to Example 2, and obtained the biaxially oriented laminated film of thickness 10 micrometers. Although the film was not inferior in characteristics as a capacitor film, the production rate in the molten sheet cooling step during production did not increase, and the use ratio of inexpensive raw materials was low. In comparison, it was disadvantageous in terms of cost.

Comparative Example 4 In the polyester (a) produced in Example 1, the specific resistance at the time of melting was 2 ×
A polyester (f) of 10 ⁸ Ωcm was obtained. A biaxially oriented polyester film having a thickness of 8 μm was obtained in the same manner as in Example 2, except that the raw material of the layer A was a raw material obtained by mixing 70 parts of the polyester (f) and 30 parts of the polyester (b). The electrical properties of the film for a capacitor were inferior.

Comparative Example 5 In Example 1, the raw material of the layer B contained 2.5% by weight of silica particles having an average particle diameter of 1.3 μm, and the specific resistance at the time of melting was 8.8.
A biaxially oriented laminated polyester film having a thickness of 9 μm was obtained in the same manner as in Example 1 except that the polyester (g) was 0 × 10 ⁸ Ω · cm. The electrical properties of the film for a capacitor were inferior.

The results obtained above are summarized in Table 1 below.
3 are shown.

[0068]

[Table 1]

[0069]

[Table 2]

[0070]

[Table 3]

[0071]

According to the present invention, a film having excellent withstand voltage and thermal dimensional stability can be obtained with good productivity and at low cost, and the film has excellent adhesion to a metal layer to be deposited. When used as a dielectric of a capacitor, it can provide high electrical properties and moisture and heat resistance and contribute to improving the long-term reliability of the capacitor, and its industrial value is high.

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Claims (4)

[Claims] 1. A method according to claim 1, wherein the content of the particles is 2.0% by weight or less and the specific resistance at the time of melting is less than 2.0 × 10 ⁹ Ωcm. Polyester (A) having a resistance higher than the melting specific resistance of polyester (B) and not less than 1.0 × 10 ⁸ Ω · cm
A laminated polyester film for a capacitor, comprising a layered polyester film having a layer A derived from the film, wherein the thickness of the layer B accounts for 30% or more of the total thickness of the film. 2. The laminated polyester film for a capacitor according to claim 1, further comprising a coating layer made of a water-soluble or water-dispersible resin and having a thickness of 0.005 μm to 0.5 μm on at least one surface. 3. The laminated polyester film for a capacitor according to claim 1, wherein the heat shrinkage stress in the longitudinal direction of the film satisfies the following expression at the same time. S150 <120 g / mm ² Smax <500 g / mm ² (in the above formula, S150 is a shrinkage stress value per unit sectional area of the film at 150 ° C., Smax is 150 ° C.)
It indicates the maximum value of the shrinkage stress value within the temperature range below the melting point of the film.) 4. The method for producing a film according to claim 1, wherein 30% by weight or more of a recycled material is blended as the polyester forming the layer B.